In a known piezoelectrically actuated fuel injector, as disclosed in EP0995901, a piezoelectric actuator is operable to control the position of a control piston which is moveable to control the pressure of fuel within a control chamber defined, in part, by a surface associated with a valve needle of the injector. Movement of the control piston to reduce the pressure of fuel within the control chamber causes the valve needle to lift away from a corresponding valve seat region in order to permit fuel to be injected through one or more nozzle outlets. Re-pressurisation of fuel pressure within the control chamber causes the valve member to be moved to re-engage the valve seating region.
A problem exists with the above configuration of fuel injector in that the sudden ejection of fuel through the nozzle outlets, together with movement of the internal injector components such as the piezoelectric actuator and the control piston, causes pressure wave activity within the fuel passages of the injector. The pressure wave activity can affect the quantity of fuel that is delivered through the nozzle outlets so that the actual volume of delivered fuel is not the same as the demanded fuel delivery volume as determined by the electrical driving signal provided to the piezoelectric actuator. Inaccuracy of the actual fuel delivery volume against demanded fuel delivery volume can cause excessive exhaust smoke emissions and increases fuel consumption both of which are undesirable.
It is an object of the invention to provide a fuel injector which does not suffer from the above problem.